During a seven-hour spacewalk, Russian cosmonauts have ripped off sections of the Soyuz spacecraft insulation to locate and take samples from a small hole that caused an air leak from the International Space Station in August.

Russian cosmonauts Sergey Prokopyev and Oleg Kononenko performed the one-of-a-kind seven-hour spacewalk to unseal the thermal lining covering the hole that appeared on Soyuz MS-09. It was patched-up by a Russian crew using a sealant repair kit back in August.

"Slashing the spacecraft with a knife makes my heart bleed," Kononenko told the Mission Control Center (MCC) as he cut through the insulation layer to find a tiny hole behind the cover. "Yes, we also observe it [the hole]," an MCC officer, responded.

Kononenko took samples of the sealant from the opening that will be sent back to Earth for further analysis on Soyuz MS-09 when the spacecraft departs the ISS on December 20.He explained that some kind of woolly yellowish-black composition has formed around the hole of the spacecraft.

Even though the damaged segment of the spacecraft is destined to burn upon re-entry, for now Kononenko has patched it up with fresh thermal insulation material.

On August 30, the ISS crew registered a sudden drop in air pressure, prompting emergency measures. The cause of the leak was soon discovered to be a two-millimeter hole in the hull of the recently docked Russian spacecraft Soyuz MS-09. To fix the problem the Russian crew applied several layers of epoxy resin, from the inside, before reinforcing the patch with another layer of sealant.

Roscosmos, the Russian space agency, believes that the spacecraft was most likely damaged with a drill and then patched with a sealant that degraded in space. But in order to determine whether that happened on the ground or while already on its orbit, they sent crew to investigate the outer side of the hole - before all traces of it burn in the atmosphere. The unusual space investigation was then further -and abruptly- delayed by an October mid-flight failure and emergency landing of Soyuz MS-10.